Recently, with rapid development of display technologies, color LCD devices, especially small-size color LCD devices, are more and more widely used in people's daily life and production, especially in fields of mobile phone, personal digital assistant (PDA), global positioning system (GPS), E-book, and digital camera. Characteristics of a color LCD device, such as brightness, contrast and view angle are displaying indexes drawing great attention.
In terms of brightness, as liquid crystal material can not emit light by itself, all the existing LCD devices need backlights for providing light.
In prior art, an LCD device as shown in FIG. 1 includes a color filter substrate 1, a thin film transistor (TFT) array substrate 2, a liquid crystal layer 350 disposed between the color filter substrate 1 and the TFT array substrate 2, a polarizer 3 and a backlight 4. The color filter substrate 1 includes a glass substrate 380, a color pixel layer 370, and a transparent conductive layer 360. The backlight 4 includes a light source 310, a backlight plate 300, a reflective film 390, a light guide plate 320, a diffusion chip 330 and a selective permeation film 340.
The polarizer 3 includes a polyvinyl alcohol (PVA) film containing iodine or other dichroic dyes, a tri-acetate cellulose (TAC) fiber film attached at two sides of the PVA film, surface protection film pasted on a front surface of the PVA film, a bonding layer and a release film added to the other surface of the PVA film. The PVA film is a main function film layer providing polarization for the polarizer 3. Due to being stretched, the PVA film normally has low mechanical properties and becomes easily frangible. As such, when polarization basic substance is stretched to be a film, a layer of TAC film is commonly attached on two sides thereof in order to prevent the PVA film from retracting back. The surface protection film is adapted to prevent the PVA film from pollution and scratch. The bonding layer and the release film are adapted to be used in a subsequent pasting process, preservation and transferring protection. Further more, a functional film layer, for example a wide view angle film, may be pasted outside the TAC film according to acquirements.
In an LCD device, the lights emitted from the backlight 4 pass through the polarizer 3, the TFT array substrate 2, the liquid crystal layer 350 and the color filter substrate 1, and then most of the lights are absorbed, which results in that an ultimate light utilization rate is less than 5%. At least 50% of light energy will be expensed when the lights permeate the polarizer 3 because, according to light wave theory, any non-polarized light will be decomposed into two polarization components whose vibration directions are mutually perpendicular, one polarization component in an incident natural light passes through the polarizer 3, and the other one polarization component is absorbed by the polarizer 3, which results in a 50% loss of light energy and greatly reduces the utilization rate of light energy.
The method for producing the polarizer 3 specifically includes the following steps:
Pre-processing which includes: performing chemical processing to the TAC film so as to strengthen adhesion force to the PVA;
Stretching which includes: first, dipping a piece of flexible transparent substrate (commonly a PVA) with chemical activity into KI water solution containing iodine molecules (I2), so that many iodine ions disperse and penetrate into an inner layer of the PVA plate within a few seconds; after heating at low temperature, stretching manually or mechanically to several times in length so that the PVA plate will become narrow and thin while it is getting longer; in which the PVA molecules are supposed to be at any angle and distributed randomly but gradually and consistently deflects in a direction of force after being stretched so that the iodine ions attached on the PVA plate will also possess directivity accordingly and form a long chain of iodine molecules. The iodine ions possess good dichroism so that they can absorb the beam field component parallel to an alignment direction thereof and only allow the beam field component in a vertical direction to pass so as to form a polarization function. The PVA film is dyed in the solution containing iodine and then pasted with the TAC film finishing the pre-processing;
Film pasting which includes: coating adhesive onto a surface of the release film for bonding glass and pasting with products finishing the stretching;
Cutting which includes: cutting products finishing film pasting into sizes desired by customers;
Checking which includes: checking size, characteristics and appearance for products finishing cutting.
The existing method for producing the polarizer is complicated and the main ingredient of the obtained polarizer is PVA and TAC which take up 70% of material used during polarizer producing which results in high cost.